Is my water heater large enough?

My condo has a 50 gallon electric water heater. Both the top and bottom burners are set to the "middle" position on the thermostat, which should be about 120F. There is JUST enough hot water (not quite) for two 10-15 minute back-to-back showers. Does that sound right? I thought that a 50 gallon tank would be plenty for just two people. Any thoughts?

To be exact, my heater is the M-2-50T6DS from Bradford-White -- specs are here. The heater is only 6 months old and the showerhead is a typical new showerhead, probably 2.5 GPM.

A tank-type water heater can deliver about 70% of its rated volume before a definite change in temperature is noted so for a 50 gallon tank that would be about 35 gallons.

A "standard" 2.5 gpm shower head would flow 25 gallons in ten minutes, 37 gallons in fifteen minutes so two back-to-back showers would take 50 to 75 gallons of water.

Of course you probably don't shower with 120 degree water, more likely 105 to 110 so you are using some cold along with the hot but still, you can't expect to get 20 to 30 minutes of shower time with just a 50 gallon heater set at 120 degrees.

What you could do is install an ultra-low-flow shower head but I doubt that you would like it, or you could raise the temperature setting of the water heater. At 140 degrees you would be blending much more cold water and that would lessen the flow rate of the hot and effectively give you more hot water. The downside is that 140 degree hot water is dangerous and can scald you in mere seconds. The answer to that is to also install a tempering valve at the water heater that will automatically blend in the cold to maintain 120 degrees (or whatever you set) delivered to the hot water piping. Yes, the tempering valve is something else to go wrong (see the posts a few down from this one) but your only other answer is shorter showers or stagger the showers to allow the water heater to recover its set temperature. Your heater is rated at a 90 degree temperature rise of 21 gallons every hour so if you run the shower to the point where it is uncomfortable it will likely take close to two hours before you can take another 15 minute shower.

I guess it's a matter of style. Are you an environmentalist concerned about global warming who thinks people driving SUVs are abusing the environment? If so, your water heater is grossly oversized ---- you should install a much smaller one.

If you want to maximize economic growth, don't care a fig about the environment and drive an SUV, you need a larger water heater.

furd - Thanks for breaking it down for me! This is very helpful. It sounds like everything is working as expected. It's just a little surprising since all the water heater "sizing tools" I've used would suggest that a 50-gallon tank is almost too much for two people. I guess we just take long showers. That sucks.

SeattlePioneer - I can only hope that this vice of mine is at least somewhat balanced by the fact that I have not owned a car in seven years and have used either public transportation or my bicycle to get around since then, including riding my bike clear through Chicago winters (brrrrr!). Hopefully, the four years I spent being grossly underpaid while working at an environmental non-profit counts for something as well. Do I still have to give up my hot water?

Good answer sawyer. My low flow shower head allows me to reduce the water flow to way below the 2.5 gallon per minute rate and it provides a hot steam effect that compensates for the reduced flow. Look around at some of the high tech shower heads, there might be one that meets your needs and reduces the hot water flow.

Since you don't really know what the water temp actually is, test it or ease it up until you judge it to be too hot. You may be running below the 120 mark. You can compensate for the increased temp by adding more insulation to the tank and or hot water pipes.

Also, having the flow control at the shower head allows me to increase and decrease the flow as my shower needs vary.

Good answer sawyer. My low flow shower head allows me to reduce the water flow to way below the 2.5 gallon per minute rate and it provides a hot steam effect that compensates for the reduced flow. Look around at some of the high tech shower heads, there might be one that meets your needs and reduces the hot water flow.

Since you don't really know what the water temp actually is, test it or ease it up until you judge it to be too hot. You may be running below the 120 mark. You can compensate for the increased temp by adding more insulation to the tank and or hot water pipes.

Bud - I measured the temp last night and my water is at about 125 which is about as high as I'd like to go...I'm wary of of just bumping up the temp as that doesn't seem efficient. A high tech showerhead sounds more desirable...don't suppose you could recommend a brand?

The one I have is older than I like to admit, but a quick google should get you some options.

As for efficiency, new water heaters are much better insulated than their predecessors that started all of the concerns about standby losses. By adding a blanket to a new one and some good pipe insulation, there would be very little wasted energy. But I agree, since I use one, a good low flow shower head is a good way to go.

There is at least some uninsulated copper coming out of the water heater that I could insulate. I have no idea how to get to the rest of it without ripping through walls/floors, but I will insulate what I can. Thanks for the tip.

If you have the right physical layout and like showers, you should consider a drain heat recovery unit. I got one primarily to be able to handle back to back to back showers in the morning and save some money. They definately work, especially when you have cold "cold" water. We have a 40 gal tank and have no problems taking multiple showers in a row. I think the pay back is good if you can DIY and primarily take showers.

Here is some govt info and brand <a href="http://www.gfxtechnology.com/VGFX.html">info</a> on mine